U.S. patent application number 12/561868 was filed with the patent office on 2011-03-17 for readout apparatus and multi-channel readout apparatus for touch panel.
This patent application is currently assigned to HIMAX TECHNOLOGIES LIMITED. Invention is credited to Ying-Lieh Chen, Kai-Lan Chuang, Guo-Ming Lee.
Application Number | 20110063233 12/561868 |
Document ID | / |
Family ID | 43730028 |
Filed Date | 2011-03-17 |
United States Patent
Application |
20110063233 |
Kind Code |
A1 |
Chuang; Kai-Lan ; et
al. |
March 17, 2011 |
READOUT APPARATUS AND MULTI-CHANNEL READOUT APPARATUS FOR TOUCH
PANEL
Abstract
A readout apparatus and a multi-channel readout apparatus for a
touch panel are provided to integrate different types of readout
circuit. The readout apparatus set to a first mode reads the touch
panel with a small amount of charges through an integrator. The
readout apparatus set to a second mode reads a sensing current of a
current type touch panel through a current to voltage converting
unit and an inverting amplifier, so as to save a chip area. The
multi-channel readout apparatus set to a third mode applies
multiple channels to alternatively share an integrator to read the
touch panel with a large amount of charges, so that an amount of
feedback capacitors (integral capacitors) having a great area can
be greatly reduced. Therefore, readout apparatus of the present
invention can not only reduce a chip area, but can also be applied
to various types of the touch panel.
Inventors: |
Chuang; Kai-Lan; (Tainan
County, TW) ; Lee; Guo-Ming; (Tainan County, TW)
; Chen; Ying-Lieh; (Tainan County, TW) |
Assignee: |
HIMAX TECHNOLOGIES LIMITED
Tainan County
TW
|
Family ID: |
43730028 |
Appl. No.: |
12/561868 |
Filed: |
September 17, 2009 |
Current U.S.
Class: |
345/173 ;
178/18.03 |
Current CPC
Class: |
G06F 3/04166
20190501 |
Class at
Publication: |
345/173 ;
178/18.03 |
International
Class: |
G06F 3/041 20060101
G06F003/041 |
Claims
1. A readout apparatus for a touch panel, comprising: a first
selector, having a common terminal electrically connected to a
first selection terminal or a second selection terminal,
selectively; a current to voltage converting unit, having an input
terminal coupled to the first selection terminal of the first
selector; a first resistor, having a first terminal coupled to an
output terminal of the current to voltage converting unit; a second
selector, having a common terminal electrically connected to a
first selection terminal or a second selection terminal,
selectively, wherein the first selection terminal of the second
selector is coupled to a second terminal of the first resistor, and
the second selection terminal of the second selector is coupled to
the second selection terminal of the first selector; a first
operation amplifier, having a first input terminal coupled to the
common terminal of the second selector, and a second input terminal
receiving a first reference voltage; a third selector, having a
common terminal electrically connected to a first selection
terminal or a second selection terminal, selectively, wherein the
common terminal of the third selector is coupled to the first input
terminal of the first operation amplifier; a fourth selector,
having a common terminal electrically connected to a first
selection terminal or a second selection terminal, selectively,
wherein the common terminal of the fourth selector is coupled to an
output terminal of the first operation amplifier; a second
resistor, having a first terminal coupled to the first selection
terminal of the third selector, and a second terminal coupled to
the first selection terminal of the fourth selector; a feedback
capacitor, having a first terminal coupled to the second selection
terminal of the third selector, and a second terminal coupled to
the second selection terminal of the fourth selector; and a
feedback switch, having a first terminal and a second terminal
respectively coupled to the first terminal and the second terminal
of the feedback capacitor.
2. The readout apparatus for the touch panel as claimed in claim 1,
wherein the current to voltage converting unit comprises: a third
resistor, having a first terminal serving as the input terminal of
the current to voltage converting unit, and a second terminal
coupled to a second reference voltage; and a unit-gain amplifier,
having an input terminal coupled to the first terminal of the third
resistor, and an output terminal serving as the output terminal of
the current to voltage converting unit.
3. The readout apparatus for the touch panel as claimed in claim 2,
wherein the unit-gain amplifier comprises a second operation
amplifier, a first terminal of the second operation amplifier
serves as the input terminal of the unit-gain amplifier, a second
terminal of the second operation amplifier is coupled to an output
terminal of the second operation amplifier, and the output terminal
of the second operation amplifier serves as the output terminal of
the unit-gain amplifier.
4. The readout apparatus for the touch panel as claimed in claim 1,
wherein the current to voltage converting unit comprises: a third
resistor, having a first terminal receiving a third reference
voltage, and a second terminal serving as the output terminal of
the current to voltage converting unit; and a current mirror,
having a master current terminal serving as the input terminal of
the current to voltage converting unit, and a slave current
terminal coupled to the second terminal of the third resistor.
5. The readout apparatus for the touch panel as claimed in claim 4,
wherein the third resistor is a transistor, a first terminal of the
transistor receives the third reference voltage, and a second
terminal and a control terminal of the transistor are coupled to
the slave current terminal of the current mirror.
6. The readout apparatus for the touch panel as claimed in claim 4,
wherein the current mirror comprises: a first transistor, having a
first terminal serving as the master current terminal of the
current mirror, a second terminal receiving a fourth reference
voltage, and a control terminal coupled to the first terminal of
the first transistor; and a second transistor, having a first
terminal serving as the slave current terminal of the current
mirror, a second terminal receiving the fourth reference voltage,
and a control terminal coupled to the control terminal of the first
transistor.
7. The readout apparatus for the touch panel as claimed in claim 6,
wherein the third reference voltage is a system voltage, and the
fourth reference voltage is a ground voltage.
8. The readout apparatus for the touch panel as claimed in claim 4,
wherein the current mirror comprises: a first transistor, having a
first terminal serving as the master current terminal of the
current mirror, and a control terminal coupled to the first
terminal of the first transistor; a second transistor, having a
first terminal serving as the slave current terminal of the current
mirror, and a control terminal coupled to the control terminal of
the first transistor; a third transistor, having a first terminal
coupled to a second terminal of the first transistor, a second
terminal receiving a fourth reference voltage, and a control
terminal coupled to the first terminal of the third transistor; and
a fourth transistor, having a first terminal coupled to a second
terminal of the second transistor, a second terminal receiving the
fourth reference voltage, and a control terminal coupled to the
control terminal of the third transistor.
9. The readout apparatus for the touch panel as claimed in claim 1,
wherein in a first mode, the first, the second, the third and the
fourth selectors respectively select to electrically connect the
common terminal thereof to the second selection terminal
thereof.
10. The readout apparatus for the touch panel as claimed in claim
1, wherein in a second mode, the first, the second, the third and
the fourth selectors respectively select to electrically connect
the common terminal thereof to the first selection terminal
thereof.
11. The readout apparatus for the touch panel as claimed in claim
1, wherein the common terminal of the first resistor is coupled to
a corresponding sensor line of the touch panel.
12. A multi-channel readout apparatus for a touch panel,
comprising: an integrator; and a plurality of channels, and each of
the channels comprising: an input selector, having a common
terminal electrically connected to a first selection terminal or a
second selection terminal, selectively, wherein the first selection
terminal of the input selector is coupled to an input terminal of
the integrator; a first selector, having a common terminal
electrically connected to a first selection terminal or a second
selection terminal, selectively, wherein the common terminal of the
first selector is coupled to the second selection terminal of the
input selector; a current to voltage converting unit, having an
input terminal coupled to the first selection terminal of the first
selector; a first resistor, having a first terminal coupled to an
output terminal of the current to voltage converting unit; a second
selector, having a common terminal electrically connected to a
first selection terminal or a second selection terminal,
selectively, wherein the first selection terminal of the second
selector is coupled to a second terminal of the first resistor, and
the second selection terminal of the second selector is coupled to
the second selection terminal of the first selector; a first
operation amplifier, having a first input terminal coupled to the
common terminal of the second selector, and a second input terminal
receiving a first reference voltage; a third selector, having a
common terminal electrically connected to a first selection
terminal or a second selection terminal, selectively, wherein the
common terminal of the third selector is coupled to the first input
terminal of the first operation amplifier; a fourth selector,
having a common terminal electrically connected to a first
selection terminal or a second selection terminal, selectively,
wherein the common terminal of the fourth selector is coupled to an
output terminal of the first operation amplifier; a second
resistor, having a first terminal coupled to the first selection
terminal of the third selector, and a second terminal coupled to
the first selection terminal of the fourth selector; a feedback
capacitor, having a first terminal coupled to the second selection
terminal of the third selector, and a second terminal coupled to
the second selection terminal of the fourth selector; a feedback
switch, having a first terminal and a second terminal respectively
coupled to the first terminal and the second terminal of the
feedback capacitor; and an output selector, having a common
terminal electrically connected to a first selection terminal or a
second selection terminal, selectively, wherein the first selection
terminal of the output selector is coupled to an output terminal of
the integrator, and the second selection terminal of the output
selector is coupled to the output terminal of the first operation
amplifier.
13. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein the current to voltage converting unit
comprises: a third resistor, having a first terminal serving as the
input terminal of the current to voltage converting unit, and a
second terminal coupled to a second reference voltage; and a
unit-gain amplifier, having an input terminal coupled to the first
terminal of the third resistor, and an output terminal serving as
the output terminal of the current to voltage converting unit.
14. The multi-channel readout apparatus for the touch panel as
claimed in claim 13, wherein the unit-gain amplifier comprises a
second operation amplifier, a first terminal of the second
operation amplifier serves as the input terminal of the unit-gain
amplifier, a second terminal of the second operation amplifier is
coupled to an output terminal of the second operation amplifier,
and the output terminal of the second operation amplifier serves as
the output terminal of the unit-gain amplifier.
15. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein the current to voltage converting unit
comprises: a third resistor, having a first terminal receiving a
third reference voltage, and a second terminal serving as the
output terminal of the current to voltage converting unit; and a
current mirror, having a master current terminal serving as the
input terminal of the current to voltage converting unit, and a
slave current terminal coupled to the second terminal of the third
resistor.
16. The multi-channel readout apparatus for the touch panel as
claimed in claim 15, wherein the third resistor is a transistor, a
first terminal of the transistor receives the third reference
voltage, and a second terminal and a control terminal of the
transistor are coupled to the slave current terminal of the current
mirror.
17. The multi-channel readout apparatus for the touch panel as
claimed in claim 15, wherein the current mirror comprises: a first
transistor, having a first terminal serving as the master current
terminal of the current mirror, a second terminal receiving a
fourth reference voltage, and a control terminal coupled to the
first terminal of the first transistor; and a second transistor,
having a first terminal serving as the slave current terminal of
the current mirror, a second terminal receiving the fourth
reference voltage, and a control terminal coupled to the control
terminal of the first transistor.
18. The multi-channel readout apparatus for the touch panel as
claimed in claim 17, wherein the third reference voltage is a
system voltage, and the fourth reference voltage is a ground
voltage.
19. The multi-channel readout apparatus for the touch panel as
claimed in claim 15, wherein the current mirror comprises: a first
transistor, having a first terminal serving as the master current
terminal of the current mirror, and a control terminal coupled to
the first terminal of the first transistor; a second transistor,
having a first terminal serving as the slave current terminal of
the current mirror, and a control terminal coupled to the control
terminal of the first transistor; a third transistor, having a
first terminal coupled to a second terminal of the first
transistor, a second terminal receiving a fourth reference voltage,
and a control terminal coupled to the first terminal of the third
transistor; and a fourth transistor, having a first terminal
coupled to a second terminal of the second transistor, a second
terminal receiving the fourth reference voltage, and a control
terminal coupled to the control terminal of the third
transistor.
20. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein in a first mode, the input selector,
the first, the second, the third and the fourth selectors and the
output selector respectively select to electrically connect the
common terminal thereof to the second selection terminal
thereof.
21. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein in a second mode, the input selector
and the output selector respectively select to electrically connect
the common terminal thereof to the second selection terminal
thereof, and the first, the second, the third and the fourth
selectors respectively select to electrically connect the common
terminal thereof to the first selection terminal thereof.
22. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein in a third mode, the first, the
second, the third and the fourth selectors respectively select to
electrically connect the common terminal thereof to the second
selection terminal thereof, and the feedback switch is turned
on.
23. The multi-channel readout apparatus for the touch panel as
claimed in claim 22, wherein during a channel period of a plurality
of channel periods in the third mode, the input selector and the
output selector of one of the channels respectively select to
electrically connect the common terminal thereof to the first
selection terminal thereof, and the input selectors and the output
selectors of the other channels respectively select to electrically
connect the common terminal thereof to the second selection
terminal thereof.
24. The multi-channel readout apparatus for the touch panel as
claimed in claim 22, wherein during the period that a current
channel period finishes and a next channel period does not yet
start, the input selectors and the output selectors of the channels
respectively select to electrically connect the common terminal
thereof to the first selection terminal thereof.
25. The multi-channel readout apparatus for the touch panel as
claimed in claim 12, wherein the common terminals of the input
selectors of the channels are coupled to corresponding sensor lines
of the touch panel respectively.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a touch apparatus. More
particularly, the present invention relates to a readout apparatus
for a touch panel.
[0003] 2. Description of Related Art
[0004] With booming development of electronic technologies, and
popularization of wireless communication and networks, various
electronic devices gradually become indispensable tools for
people's daily life. However, operation of a commonly used
input/output (I/O) interface such as a keyboard or a mouse is
rather difficult. Comparatively, a touch panel is an intuitive and
simple I/O interface. Therefore, the touch panel is generally used
as a human-machine interface between a user and an electronic
device to facilitate control operations.
[0005] Generally, the touch panels are grouped into resistive touch
panels, photo touch panels and capacitive touch panels, etc.
Considering a readout approach, the touch panels are grouped into
current type touch panels and charge type touch panels, etc. FIG. 1
is a schematic diagram illustrating a photo charge type touch panel
and a conventional readout circuit. A plurality of data lines and a
plurality of scan lines of the photo charge type touch panel 110
are respectively driven by a source driver 120 and a gate driver
130, and a plurality of sensor lines of the photo charge type touch
panel 110 is coupled to a plurality of readout circuits 140. Only
one of the scan lines, one of the data lines and one of the sensor
lines are illustrated in FIG. 1.
[0006] A storage capacitor Cst1 and a liquid crystal capacitor Clc
are respectively coupled to a bias voltage V.sub.BIAS1 and a common
voltage V.sub.COM. The bias voltage V.sub.BIAS1 and a common
voltage V.sub.COM can be same or difference voltage(s). When the
gate driver 130 turns on a switch SW1 through the scan line, the
source driver 120 writes pixel data into the storage capacitor Cst1
and the liquid crystal capacitor Clc through the data line. Since a
voltage difference between the pixel data and the common voltage
V.sub.COM correspondingly deflects liquid crystal molecules in the
liquid crystal capacitor Clc, the pixel may have a corresponding
gray level.
[0007] Based on a bias voltage V.sub.BIAS2, a photo transistor PT
provides a discharge path between a storage capacitor Cst2 and the
bias voltage V.sub.BIAS2. If a position where the photo transistor
PT is located is not touched by the user, the photo transistor PT
accelerates discharging the storage capacitor Cst2 due to
irradiation of an external light. Conversely, if the external light
irradiating on the photo transistor PT is reduced due to a user's
touch, the photo transistor PT slows down discharging the storage
capacitor Cst2. When the gate driver 130 turns on a switch SW2
through one of the scan lines, the readout circuit 140 reads the
remained charge quantity of the storage capacitor Cst2 through one
of the sensor lines, and simultaneously charges the storage
capacitor Cst2 to a normal rated voltage level.
[0008] When the readout circuit 140 detects the photo charge type
touch panel 110, a position touched by the user is mainly
determined according to inconsistent discharge of the storage
capacitor Cst2 or whether there is a coupling capacitor. Regarding
the photo charge type touch panel 110, an integrator (i.e. an
operation amplifier 141 and a feedback capacitor Cfb) is generally
configured in the readout circuit 140 to detect a charge difference
of the photo charge type touch panel 110. An analog-to-digital
converter (ADC) 143 converts an integration result of the
integrator into a corresponding digital code, and transmits the
digital code to an image processing circuit 150 for determining the
touch position.
[0009] FIG. 2 is a schematic diagram illustrating a photo current
type touch panel and a conventional readout circuit. A plurality of
scan lines of the touch panel 210 is driven by the gate driver 130,
and a plurality of sensor lines of the touch panel 210 is coupled
to a readout circuit 240. A pixel layout of the conventional photo
current type touch panel 210 is as that shown in FIG. 2. Each of
the pixels has a switch SW1 and a photo transistor PT. When the
bias voltage V.sub.BIAS is higher than a voltage of a node A and
the gate driver 130 turns on the switch SW1 through the scan line,
a sensing current Is will flow to the sensor line through the photo
transistor PT and the switch SW1, due to the fact that the photo
transistor PT is in a forward-bias state. Wherein, an intensity of
the light irradiating on the photo transistor PT can influence an
amount of the sensing current Is.
[0010] The readout circuit 240 is used to detect the amount and a
difference of the sensing current Is on each of the sensor lines,
so as to determine whether a light-shielding object is located at a
corresponding position of the touch panel 210 (i.e. whether an
external object touches the touch panel 210). The readout circuit
240 transmits a detection result in form of the digital code to the
image processing circuit 150. The image processing circuit 150 then
determines the touch position according to all of the digital codes
provided by the readout circuit 240. The conventional readout
circuit 240 uses an integrator (i.e. an operation amplifier 241 and
a feedback capacitor Cfb) to convert the sensing current Is into a
corresponding voltage, and then an ADC 243 converts the voltage
into a corresponding digital code, and transmits the digital code
to the image processing circuit 150 for determining the touch
position.
[0011] FIG. 3 is a schematic diagram illustrating a capacitive
touch panel and a conventional readout circuit. The capacitive
touch panel 310 has a plurality of sensor lines in a Y-axis
direction and a plurality of sensor lines in an X-axis direction. A
coupling capacitor Cp is formed between each of the Y-axis
direction sensor lines and each of the X-axis direction sensor
lines. An integrator 320 including an operation amplifier 322 and a
feedback capacitor Cfb is configured to each of the sensor lines.
In the beginning, positive input terminals of all of the operation
amplifiers 322 receive a 0V (volt) reference voltage Vref, and all
of switches 323 are turned on, so that all of the sensor lines are
charged to 0V. Thereafter, the integrators 320 turn off the
switches 323 to perform readout operations. During a period when
the switches 323 are turned off, assuming no conductor (for
example, a finger) touches the touch panel 310, when the reference
voltage Vref is transited from 0V to 5V, the integrators 320 in the
Y-axis direction and the X-axis direction can equalize the voltages
at two ends of the coupling capacitor Cp to 5V. Since
charge/discharge of the coupling capacitors Cp is not required,
when the reference voltage Vref is transited to 5V, such variation
is reflected on an output of the integrator 320. After the
integrators 320 complete the readout operations, all of the
switches 323 are again turned on, and the above operations are
repeated.
[0012] When the conductor (for example, the finger) touches the
touch panel 310, an extra capacitor Cf is formed at the
corresponding touch position as that shown in FIG. 3. During a
period when the switches 323 are turned off, when the reference
voltage Vref is transferred from 0V to 5V, the corresponding
integrator 320 charges/discharges the extra capacitor Cf through
the sensing line. Therefore, when the reference voltage Vref is
transferred to 5V, an output OUT of the integrator 320
corresponding to the extra capacitor Cf is varied, and a formula
thereof is OUT=5+[(5V-0V).times.Cf]/Cfb. Then, the integrator 320
transmits the readout result to a follow-up circuit (including the
ADC and the image processing circuit that are not illustrated) for
determining coordinates of the touch position. According to a
difference between a signal read by the sensor line having the
extra capacitor Cf and a signal read by the sensor line without the
extra capacitor Cf, the touch position can be determined. According
to the above formula, it is known that the larger the extra
capacitor Cf is, the larger the feedback capacitor Cfb is,
otherwise, the output of the integrator 320 is easy to be
saturated, and the touch position cannot be determined.
[0013] However, to avoid the saturation of the output of the
integrator, capacitances of the feedback capacitors Cfb in the
integrators has to be increased (i.e. the areas of the capacitors
have to be increased). Since each of the sensor lines requires an
integrator, a chip area occupied by the integrators is
considerable. Moreover, different types of the touch panel require
the readout circuits of different functions to read the signals of
the touch panels and convert the signals into the digital signals
that can be operated by the follow-up image processing circuits.
For example, a capacitance of the feedback capacitor Cfb of FIG. 3
is much bigger than a capacitance of the feedback capacitor Cfb, so
that the readout circuit 140 applied to the photo charge type touch
panel 110 cannot be applied to the capacitive touch panel 310. If
each type of the touch panel applies the readout circuit of a
different function, a usage flexibility of the readout apparatus of
the touch panel is relatively low.
SUMMARY OF THE INVENTION
[0014] The present invention is directed to a readout apparatus and
a multi-channel readout apparatus for a touch panel, which can be
applied to different types of the touch panel.
[0015] The present invention provides a readout apparatus for a
touch panel, which includes a first selector, a second selector, a
third selector, a fourth selector, a current to voltage converting
unit, a first resistor, a second resistor, a first operation
amplifier, a feedback capacitor and a feedback switch. A common
terminal of each of the selectors is electrically connected to a
first selection terminal or a second selection terminal,
selectively. An input terminal of the current to voltage converting
unit is coupled to the first selection terminal of the first
selector. A first terminal of the first resistor is coupled to an
output terminal of the current to voltage converting unit. The
first selection terminal of the second selector is coupled to a
second terminal of the first resistor, and the second selection
terminal of the second selector is coupled to the second selection
terminal of the first selector. A first input terminal of the first
operation amplifier is coupled to the common terminal of the second
selector, and a second input terminal of the first operation
amplifier receives a reference voltage. The common terminal of the
third selector is coupled to the first input terminal of the first
operation amplifier. The common terminal of the fourth selector is
coupled to an output terminal of the first operation amplifier. A
first terminal of the second resistor is coupled to the first
selection terminal of the third selector, and a second terminal of
the second resistor is coupled to the first selection terminal of
the fourth selector. A first terminal of the feedback capacitor is
coupled to the second selection terminal of the third selector, and
a second terminal of the feedback capacitor is coupled to the
second selection terminal of the fourth selector. A first terminal
and a second terminal of the feedback switch are respectively
coupled to the first terminal and the second terminal of the
feedback capacitor.
[0016] The present invention provides a multi-channel readout
apparatus for a touch panel. The multi-channel readout apparatus
includes an integrator and a plurality of channels. Each channel
includes an input selector, a first selector, a second selector, a
third selector, a fourth selector, a current to voltage converting
unit, a first resistor, a second resistor, a first operation
amplifier, a feedback capacitor, a feedback switch and an output
selector. A common terminal of each of the selectors is
electrically connected to a first selection terminal or a second
selection terminal, selectively. The first selection terminal of
the input selector is coupled to an input terminal of the
integrator. The common terminal of the first selector is coupled to
the second selection terminal of the input selector. An input
terminal of the current to voltage converting unit is coupled to
the first selection terminal of the first selector. A first
terminal of the first resistor is coupled to an output terminal of
the current to voltage converting unit. The first selection
terminal of the second selector is coupled to a second terminal of
the first resistor, and the second selection terminal of the second
selector is coupled to the second selection terminal of the first
selector. A first input terminal of the first operation amplifier
is coupled to the common terminal of the second selector, and a
second input terminal of the first operation amplifier receives a
reference voltage. The common terminal of the third selector is
coupled to the first input terminal of the first operation
amplifier. The common terminal of the fourth selector is coupled to
an output terminal of the first operation amplifier. A first
terminal of the second resistor is coupled to the first selection
terminal of the third selector, and a second terminal of the second
resistor is coupled to the first selection terminal of the fourth
selector. A first terminal of the feedback capacitor is coupled to
the second selection terminal of the third selector, and a second
terminal of the feedback capacitor is coupled to the second
selection terminal of the fourth selector. A first terminal and a
second terminal of the feedback switch are respectively coupled to
the first terminal and the second terminal of the feedback
capacitor. The first selection terminal of the output selector is
coupled to an output terminal of the integrator, and the second
selection terminal of the output selector is coupled to the output
terminal of the first operation amplifier.
[0017] In an embodiment of the present invention, in a first mode,
the input selector, the first selector, the second selector, the
third selector, the fourth selector and the output selector
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof.
[0018] In an embodiment of the present invention, in a second mode,
the input selector, the first selector, the second selector, the
third selector, the fourth selector and the output selector
respectively select to electrically connect the common terminal
thereof to the first selection terminal thereof.
[0019] In an embodiment of the present invention, in a third mode,
the first selector, the second selector, the third selector and the
fourth selector respectively select to electrically connect the
common terminal thereof to the second selection terminal thereof,
and the feedback switch is turned on. In the third mode, the input
selector and the output selector of one of the channels
respectively select to electrically connect the common terminal
thereof to the first selection terminal thereof, and the input
selectors and the output selectors of the other channels
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof.
[0020] In the present invention, the readout circuits of different
types are integrated. The current to voltage converting unit and an
inverting amplifier are used to read the sensing current of the
current type touch panel, so that utilization of integral
capacitors is avoided and a chip area occupied by the feedback
capacitors is reduced. In some embodiments, multiple channels can
alternately share a common integrator to read the sensing charges
of the capacitive touch panel, so that an area of the feedback
capacitor (integral capacitor) can be greatly reduced. Therefore,
readout apparatus of the present invention can not only reduce a
chip area, but can also be applied to various types of the touch
panel.
[0021] In order to make the aforementioned and other features and
advantages of the present invention comprehensible, several
exemplary embodiments accompanied with figures are described in
detail below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings are included to provide a further
understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
embodiments of the invention and, together with the description,
serve to explain the principles of the invention.
[0023] FIG. 1 is a schematic diagram illustrating a photo charge
type touch panel and a conventional readout circuit.
[0024] FIG. 2 is a schematic diagram illustrating a photo current
type touch panel and a conventional readout circuit.
[0025] FIG. 3 is a schematic diagram illustrating a capacitive
touch panel and a conventional readout circuit.
[0026] FIG. 4 is a circuit schematic diagram illustrating a readout
apparatus of a touch panel according to an embodiment of the
present invention.
[0027] FIG. 5 is an equivalent circuit diagram of a readout
apparatus of FIG. 4 that is set to a first mode according to an
embodiment of the present invention.
[0028] FIG. 6 is an equivalent circuit diagram of a readout
apparatus of FIG. 4 that is set to a second mode according to an
embodiment of the present invention.
[0029] FIG. 7 is another circuit diagram of a current to voltage
converting unit of FIG. 4 according to an embodiment of the present
invention.
[0030] FIG. 8 is still another circuit diagram of a current to
voltage converting unit of FIG. 4 according to an embodiment of the
present invention.
[0031] FIG. 9 is a circuit diagram of a multi-channel readout
apparatus of a touch panel according to another embodiment of the
present invention.
[0032] FIG. 10 is an equivalent circuit diagram of a readout
apparatus of FIG. 9 that is set to a third mode according to an
embodiment of the present invention.
[0033] FIG. 11 is a diagram showing wave form of reset signal and
reference voltage in the embodiments of the present invention.
DESCRIPTION OF THE EMBODIMENTS
[0034] In the following embodiments, a photo charge type touch
panel and a photo current type touch panel are taken as an example
for describing applications of readout apparatus of the present
invention. However, application of the present invention is not
limited thereto.
[0035] FIG. 4 is a circuit schematic diagram illustrating a readout
apparatus 400 of a touch panel according to an embodiment of the
present invention. An input terminal of the readout apparatus 400
is coupled to sensor lines of the touch panel 401, and an output
terminal of the readout apparatus 400 transmits a readout result to
a follow-up circuit (including an analog-to-digital converter (ADC)
and an image processing circuit, which are not illustrated) for
determining coordinates of a touch position. The touch panel 401
can be a charge type touch panel (for example, the photo charge
type touch panel 110 shown in FIG. 1), or a current type touch
panel (for example, the photo current type touch panel 210 shown in
FIG. 2).
[0036] The readout apparatus 400 includes a first selector 411, a
second selector 412, a third selector 413, a fourth selector 414, a
current to voltage converting unit 420, a first resistor R1, a
second resistor R2, a first operation amplifier OP1, a feedback
capacitor Cfb and a feedback switch SWfb. A common terminal of each
of the selectors 411-414 is electrically connected to a first
selection terminal or a second selection terminal, selectively. For
example, the selector 411 can electrically connect the common
terminal thereof to the first selection terminal thereof, or
electrically connect the common terminal to the second selection
terminal thereof. In the present embodiment, the selectors 411 and
413 are demultiplexers, and the selectors 412 and 414 are
multiplexers.
[0037] The common terminal of the selector 411 is coupled to the
corresponding sensor line of the touch panel 401. An input terminal
of the current to voltage converting unit 420 is coupled to the
first selection terminal of the selector 411. A first terminal of
the resistor R1 is coupled to an output terminal of the current to
voltage converting unit 420 and a second terminal of the resistor
R1 is coupled to the first selection terminal of the selector 412.
The second selection terminal of the selector 412 is coupled to the
second selection terminal of the selector 411. A first input
terminal of the operation amplifier OP1 is coupled to the common
terminal of the selector 412, and a second input terminal of the
operation amplifier OP1 receives a first reference voltage Vref. In
the present embodiment, the first input terminal of the operation
amplifier OP1 is an inverting input terminal, and the second input
terminal of the operation amplifier OP1 is a non-inverting input
terminal, and an output terminal of the operation amplifier OP1
transmits a readout result to a follow-up circuit (not illustrated)
for determining coordinates of a touch position.
[0038] A voltage level of the reference voltage Vref can be
determined according to a design requirement of a user and the type
of the touch panel 401. For example, the reference voltage Vref is
set to be a half of a system voltage VDDA (i.e. VDDA/2), or is set
to be a band-gap voltage, or is set to be +5V or other fixed
voltages. In some embodiments, the reference voltage Vref can be
set to be a time-varying voltage corresponding to a reset signal
RESET. FIG. 11 is a diagram showing wave form of the reset signal
RESET and the reference voltage Vref in the embodiment. When the
reset signal RESET has a logic low level, the reference voltage
Vref is a ground voltage (i.e. 0V), and after the reset signal
RESET is transferred to a logic high level, the reference voltage
Vref is transferred to half level of the system voltage VDDA (i.e.
VDDA/2, for example, +5V) in response to the reset signal
RESET.
[0039] The common terminal of the selector 413 is coupled to the
first input terminal of the operation amplifier OP1. The common
terminal of the selector 414 is coupled to the output terminal of
the operation amplifier OP1. A first terminal of the resistor R2 is
coupled to the first selection terminal of the selector 413, and a
second terminal of the resistor R2 is coupled to the first
selection terminal of the selector 414. A first terminal of the
feedback capacitor Cfb is coupled to the second selection terminal
of the selector 413, and a second terminal of the feedback
capacitor Cfb is coupled to the second selection terminal of the
selector 414. A first terminal and a second terminal of the
feedback switch SWfb are respectively coupled to the first terminal
and the second terminal of the feedback capacitor Cfb. The feedback
switch SWfb is controlled by a signal RESETB inverted from the
reset signal RESET.
[0040] In a first mode, the selectors 411-414 respectively select
to electrically connect the common terminal thereof to the second
selection terminal thereof. In the first mode, when the feedback
switch SWfb is turned off, the operation amplifier OP1 and the
feedback capacitor Cfb form an integrator. The readout apparatus
400 set to the first mode can read the sensing signals of the photo
charge type touch panel 110.
[0041] FIG. 5 is an equivalent circuit diagram of the readout
apparatus 400 of FIG. 4 that is set to the first mode according to
an embodiment of the present invention. The touch panel 401 is
assumed to be the photo charge type touch panel 110 shown in FIG.
1. During a period when the system is initially powered on, or
during a reset period of the system, the system sets the reset
signal RESET to an enabling state (which may have a logic low
level). When the reset signal RESET has the logic low level (i.e.
the signal RESETB is set to the logic high level), the feedback
switch SWfb is turned on to reset the feedback capacitor Cfb. When
the reset signal RESET is in a disabling state (for example, has a
logic high level, i.e. the signal RESETB is set to the logic low
level), and the switch SW2 is turned on, the integrator can perform
an integration operation to the sensor line of the touch panel 110
(i.e. the touch panel 401), and then the operation amplifier OP1
transmits the readout result to the follow-up circuit (not
illustrated) for determining the coordinates of the touch
position.
[0042] Referring to FIG. 4, in a second mode, the selectors 411-414
respectively select to electrically connect the common terminal
thereof to the first selection terminal thereof. In the second
mode, the readout apparatus 400 can be regarded as a readout
circuit formed by the current to voltage converting unit 420 and an
inverting amplifier 610. The readout apparatus 400 set to the
second mode can read the sensing signals of the photo current type
touch panel 210.
[0043] FIG. 6 is an equivalent circuit diagram of the readout
apparatus 400 of FIG. 4 that is set to the second mode according to
an embodiment of the present invention. The touch panel 401 is
assumed to be the photo current type touch panel 210 shown in FIG.
2. The current to voltage converting unit 420 converts a sensing
current Is of the current type touch panel 210 into a sensing
voltage Vs. An input terminal of the inverting amplifier 610 formed
by the resistors R1, R2 and the operation amplifier OP1 is coupled
to the output terminal of the current to voltage converting unit
420 for receiving the sensing voltage Vs. After the inverting
amplifier 610 gains the sensing voltage Vs, the readout result is
transmitted to the follow-up circuit (not illustrated) for
determining the coordinates of the touch position.
[0044] In the present embodiment, the current to voltage converting
unit 410 includes a third resistor 421 and a unit-gain amplifier,
wherein the unit-gain amplifier is implemented by an operation
amplifier 422. A first terminal of the resistor 421 serves as the
input terminal of the current to voltage converting unit 420, and a
second terminal of the resistor 421 is coupled to a second
reference voltage (for example, the ground voltage). A first
terminal of the operation amplifier 422 (i.e. an input terminal of
the unit-gain amplifier) is coupled to the first terminal of the
resistor 421, a second terminal of the operation amplifier 422 is
coupled to an output terminal of the operation amplifier 422 (i.e.
an output terminal of the unit-gain amplifier), and the output
terminal of the operation amplifier 422 serves as the output
terminal of the current to voltage converting unit 420. To meet
different characteristics of different touch panels, the resistors
421, R1 and/or R2 can be implemented by variable resistors
according to a design requirement of the user.
[0045] FIG. 7 is another circuit diagram of the current to voltage
converting unit 420 of FIG. 4 according to an embodiment of the
present invention. The current to voltage converting unit 420
includes a resistor 710 and a current mirror 720. A first terminal
of the resistor 710 receives a third reference voltage (for
example, the system voltage VDDA), and a second terminal of the
resistor 710 is coupled to the resistor R1. Here, the resistor 710
is implemented by a P-channel metal oxide semiconductor (PMOS)
transistor 711 for reducing a chip area occupied by the resistor
710. A first terminal (for example, a source) of the transistor 711
receives the system voltage VDDA, and a second terminal (for
example, a drain) and a control terminal (for example, a gate) of
the transistor 711 are coupled to the resistor R1.
[0046] A master current terminal of the current mirror 720 receives
the sensing current Is, and a slave current terminal of the current
mirror 720 is coupled to the second terminal of the resistor 710.
By setting a current ratio between the master current terminal and
the slave current terminal of the current mirror 720, the current
mirror 720 can amplify the weak sensing current Is. The amplified
sensing current Is can be converted into the sensing voltage Vs
through the resistor 710. By such means, in case that a photo
transistor PT is irradiated by a strong light and a weak light, a
variation range of the obtained sensing voltage Vs is increased, so
that a recognition degree of the sensing voltage Vs can be
increased. The sensing voltage Vs is again amplified by the
inverting amplifier 610 to facilitate a follow-up processing.
[0047] The current mirror 720 includes a first transistor 721 and a
second transistor 722. In the present embodiment, the transistors
721 and 722 are implemented by N-channel metal oxide semiconductor
(NMOS) transistors. A first terminal (for example, a drain) of the
transistor 721 serves as the master current terminal of the current
mirror 720, a second terminal (for example, a source) of the
transistor 721 receives a fourth reference voltage (for example,
the ground voltage), and a control terminal (for example, a gate)
of the transistor 721 is coupled to the first terminal of the
transistor 721. A first terminal of the transistor 722 serves as
the slave current terminal of the current mirror 720, a second
terminal of the transistor 722 receives the fourth reference
voltage (the ground voltage), and a control terminal of the
transistor 722 is coupled to the control terminal of the transistor
721. The current ratio between the master current terminal and the
slave current terminal of the current mirror 720 can be set by
determining an aspect ratio of the transistors 721 and 722.
[0048] FIG. 8 is still another circuit diagram of the current to
voltage converting unit 420 of FIG. 4 according to an embodiment of
the present invention. The present embodiment is similar to the
embodiment of FIG. 7, so that a part of the descriptions are not
repeated. A current mirror 730 is used to replace the
aforementioned current mirror 720. The current mirror 730 includes
a first transistor 731, a second transistor 732, a third transistor
733 and a fourth transistor 734. A first terminal (for example, a
drain) of the transistor 731 serves as a master current terminal of
the current mirror 730, and a control terminal (for example, a
gate) of the transistor 731 is coupled to the first terminal of the
transistor 731. A first terminal (for example, a drain) of the
transistor 732 serves as a slave current terminal of the current
mirror 730, and a control terminal (for example, a gate) of the
transistor 732 is coupled to the control terminal of the transistor
731. A first terminal (for example, a drain) of the transistor 733
is coupled to a second terminal (for example, a source) of the
transistor 731, a second terminal (for example, a source) of the
transistor 733 receives the reference voltage (for example, the
ground voltage), and a control terminal (for example, a gate) of
the transistor 733 is coupled to the first terminal of the
transistor 733. A first terminal (for example, a drain) of the
transistor 734 is coupled to a second terminal (for example, a
source) of the transistor 732, a second terminal (for example, a
source) of the transistor 734 receives the reference voltage (for
example, the ground voltage), and a control terminal (for example,
a gate) of the transistor 734 is coupled to the control terminal of
the transistor 733.
[0049] FIG. 9 is a circuit diagram of a multi-channel readout
apparatus 900 of a touch panel according to another embodiment of
the present invention. The readout apparatus 900 has a plurality of
channels, an input terminal of each channel is coupled to the
corresponding sensor line of the touch panel 901, and an output
terminal of each channel transmits a readout result to a follow-up
circuit (including the ADC and the image processing circuit, which
are not illustrated) for determining the coordinates of the touch
position. The touch panel 901 can be the photo charge type touch
panel 110, the photo current type touch panel 210, the capacitive
touch panel 310 or other types of the touch panel.
[0050] The multi-channel readout apparatus 900 includes an
integrator 910 and a plurality of the channels, wherein each of the
channels includes an input selector, a single-channel readout
apparatus (for example, the readout apparatus 400 of FIG. 4) and an
output selector. For example, a first channel includes an input
selector 920-1, a single-channel readout apparatus 400-1 and an
output selector 930-1. A second channel includes an input selector
920-2, a single-channel readout apparatus 400-2 and an output
selector 930-2. Deduced by analogy, an n.sup.th channel includes an
input selector 920-n, a single-channel readout apparatus 400-n and
an output selector 930-n. A common terminal of each of the
selectors 920-1.about.920-n and 930-1.about.930-n is electrically
connected to a first selection terminal or a second selection
terminal, selectively. For example, the input selector 920-1 can
electrically connect the common terminal thereof to the first
selection terminal thereof, or can electrically connect the common
terminal to the second selection terminal thereof. In the present
embodiment, the input selectors 920-1.about.920-n are
demultiplexers, and the output selectors 930-1.about.930-n are
multiplexers.
[0051] The integrator 910 includes an operation amplifier OP3, a
feedback capacitor 912 and a feedback switch 911. An input first
terminal of the operation amplifier OP3 is coupled to the first
selection terminals of the input selectors 920-1.about.920-n of all
of the channels. A first terminal and a second terminal of the
feedback capacitor 912 are respectively coupled to an inverting
input terminal and an output terminal of the operation amplifier
OP3. A first terminal and a second terminal of the feedback switch
911 are also respectively coupled to the inverting input terminal
and the output terminal of the operation amplifier OP3. A
non-inverting input terminal of the operation amplifier OP3
receives the reference voltage Vref. Here, a capacitance (or an
area) of the feedback capacitor 912 is much bigger than a
capacitance (or an area) of the feedback capacitor Cfb in each of
the channels.
[0052] In the present embodiment, an implementing method of each of
the single-channel readout apparatus 400-1.about.400-n is similar
to that of the readout apparatus 400 of FIG. 4, and therefore
detail descriptions thereof are not repeated. Moreover, the first
channel is described in detail below, and descriptions of the other
channels can be deduced by analogy according to the descriptions of
the first channel.
[0053] In the first channel, the common terminal of the input
selector 920-1 is coupled to the corresponding sensor line (for
example, a first sensor line) of the touch panel 901. The first
selection terminal of the input selector 920-1 is coupled to the
input terminal of the integrator 910, and the second selection
terminal of the input selector 920-1 is coupled to the common
terminal of the selector 411 in the single-channel readout
apparatus 400-1. The first selection terminal of the output
selector 930-1 is coupled to the output terminal of the integrator
910, and the second selection terminal of the output selector 930-1
is coupled to the output terminal of the first operation amplifier
OP1 in the single-channel readout apparatus 400-1.
[0054] The touch panel 901 corresponding to the first mode can be
the photo charge type touch panel 110 of FIG. 1. In the first mode,
the input selectors 920-1.about.920-n, the selectors 411-414 and
the output selectors 930-1.about.930-n of all of the channels
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof. In the first
mode, when the feedback switch SWfb is turned off, the operation
amplifier OP1 and the feedback capacitor Cfb form an integrator.
Each of the channels of the multi-channel readout apparatus 900 set
to the first mode can be equivalent to the integrator shown in FIG.
5 (i.e. the readout apparatus 400 in FIG. 5). Therefore, the
multi-channel readout apparatus 900 set to the first mode can read
the sensing signals from the photo charge type touch panel 110, and
transmit the readout result to the follow-up circuit (not
illustrated) through the output selectors 930-1.about.930-n for
determining the coordinates of the touch position.
[0055] Referring to FIG. 9, the touch panel 901 corresponding to
the second mode can be the photo current type touch panel 210 of
FIG. 2. In the second mode, the input selectors 920-1.about.920-n,
and the output selectors 930-1.about.930-n of all of the channels
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof, and the selectors
411-414 respectively select to electrically connect the common
terminal thereof to the first selection terminal thereof. In the
second mode, each of the channels of the multi-channel readout
apparatus 900 can be regarded as a readout circuit formed by the
current to voltage converting unit 420 and the inverting amplifier
610, as that shown in FIG. 6. Therefore, the current to voltage
converting unit 420 can convert the sensing current Is of the
current type touch panel 210 into the sensing voltage Vs. After the
inverting amplifier 610 formed by the resistor R1, the resistor R2
and the operation amplifier OP1 gains the sensing voltage Vs, the
readout result is transmitted to the follow-up circuit (not
illustrated) through the output selectors 930-1.about.930-n for
determining the coordinates of the touch position.
[0056] Referring to FIG. 9, the touch panel 901 corresponding to
the third mode can be the capacitive touch panel 310 of FIG. 3. In
the third mode, the selectors 411-414 of each of the channels
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof, and the feedback
switch SWfb of each of the channels is turned on. Therefore, the
readout apparatus 400-1.about.400-n of the channels can
respectively form a unit-gain amplifier, as that shown in FIG.
10.
[0057] FIG. 10 is an equivalent circuit diagram of the readout
apparatus 900 of FIG. 9 that is set to the third mode according to
an embodiment of the present invention. The touch panel 901 is
assumed to be the capacitive touch panel 310 of FIG. 3. Referring
to FIG. 10, during a period when the system is initially powered
on, or during a reset period of the system, the system sets the
reset signal RESET to an enabling state (which may have the logic
low level), and the input selectors 920-1.about.920-n and the
output selectors 930-1.about.930-n of all of the channels
respectively select to electrically connect the common terminal
thereof to the second selection terminal thereof. When the reset
signal RESET has the logic low level (i.e. the signal RESETB is set
to the logic-high level), the feedback switch 911 is turned on to
reset the feedback capacitor 912.
[0058] Referring to FIG. 10 and FIG. 11, during a first channel
period T1, the system sets the reset signal RESET to the logic high
level (i.e. the signal RESETB is set to the logic-low level), the
input selector 920-1 and the output selector 930-1 of the first
channel respectively select to electrically connect the common
terminal thereof to the first selection terminal thereof, and the
input selectors (for example, the input selector 920-n) and the
output selectors (for example, the output selector 930-n) of the
other channels respectively select to electrically connect the
common terminal thereof to the second selection terminal thereof.
Therefore, during the first channel period T1, the first channel
can use the integrator 910. When the reset signal RESET has the
logic high level to turn off the switch 911, the integrator 910 can
perform the integration operation to the sensor line of the touch
panel 310 (i.e. the touch panel 901), and then the operation
amplifier OP3 transmits the readout result to the follow-up circuit
(not illustrated) through the output selector 930-1 for determining
the coordinates of the touch position. During the first channel
period T1, besides the first channel, the other channels can couple
the input terminals of the internal unit-gain amplifiers (i.e. the
readout apparatus 400-2.about.400-n) to the corresponding sensor
lines of the touch panel 310.
[0059] During the period that a current channel period (e.g. the
first channel period T1 finishes and a next channel period (e.g. a
second channel period T2) does not yet start (equivalent to the
reset period), the system set the reset signal RESET to the logic
low level as shown in FIG. 11, so that the feedback switch 911 is
turned on to reset the feedback capacitor 912. During this period,
the input selectors 920-1.about.920-n and the output selectors
930-1.about.930-n of all of the channels respectively select to
electrically connect the common terminal thereof to the second
selection terminal thereof, so that the unit-gain amplifiers (i.e.
the readout apparatus 400-1.about.400-n) are coupled to the sensor
lines of the touch panel 110.
[0060] Thereafter, the second channel period T2 is entered. During
the second channel period T2, the second channel (which is not
illustrated in FIG. 10, though the second channel can be deduced
according to the related descriptions of the first channel) can use
the integrator 910, and the other channels can couple the input
terminals of the internal unit-gain amplifiers to the corresponding
sensor lines of the touch panel 310 for replacing the input
terminal of the integrator. Deduced by analogy, during an n.sup.th
channel period Tn, the n.sup.th channel can use the integrator 910,
and the other channels can couple the input terminals of the
internal unit-gain amplifiers to the corresponding sensor lines of
the touch panel 110. Detail operations of the readout apparatus
during the second channel period T2, . . . , the n.sup.th channel
period Tn are the same to that of the readout apparatus during the
first channel period T1, and therefore detail operations thereof
are not repeated.
[0061] In summary, according to the aforementioned embodiment,
different types of the readout circuit are integrated. When the
multi-channel readout apparatus 900 is set to the second mode, the
multi-channel readout apparatus 900 uses the current to voltage
converting unit 420 and the inverting amplifier to read the sensing
current of the current type touch panel, so as to avoid using the
integral capacitor and reduce the chip area occupied by the
feedback capacitors. In the third mode, the multiple channels of
the multi-channel readout apparatus 900 can alternately share a
common integrator to read the sensing charges of the capacitive
touch panel, so that an area of the feedback capacitor (integral
capacitor) can be greatly reduced. Therefore, the multi-channel
readout apparatus 900 of the present invention can not only reduce
a chip area, but can also be applied to various types of the touch
panel.
[0062] It will be apparent to those skilled in the art that various
modifications and variations can be made to the structure of the
present invention without departing from the scope or spirit of the
invention. In view of the foregoing, it is intended that the
present invention cover modifications and variations of this
invention provided they fall within the scope of the following
claims and their equivalents.
* * * * *